JP2008064621A - Particle sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor usable for on-board diagnosis of particles. <P>SOLUTION: This particle sensor includes a particle collection means for collecting particles on a part of a section vertical to a gas channel or on the second channel different from the gas channel, and at least two electrodes provided on the particle collection means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a particulate matter (PM) sensor, and more particularly to a particulate sensor that can be used for on-board diagnosis (OBD) for particulate emission detection and particulate regulation in an exhaust system of an internal combustion engine.

  Emission regulations for harmful substances contained in automobile exhaust gas are becoming stricter, and it is said that in-vehicle diagnostic equipment for emissions will be essential in the United States in 2010.

  There is also a report that even if it is a gasoline vehicle, if the fuel is directly injected into the cylinder, more particulates (PM) are discharged than a diesel vehicle equipped with a particulate filter (DPF). .

  In Patent Document 1, light emitted from a light source is transmitted through an exhaust gas flow and received by a light receiving unit, and the light opacity of exhaust gas having a constant correlation function with the particulate concentration. A technique is disclosed in which this is detected and converted to a particulate concentration by a control means.

Patent Document 2 discloses a method for detecting the amount of accumulated particulate matter by detecting a differential pressure between exhaust pressures before and after the filter due to filter pressure loss using a differential pressure sensor and determining the amount of deposited particulate matter based on the detected differential pressure. ing. Also known is a method (modeling method) for estimating the amount of particulates deposited on a filter by using the prediction of the amount of particulates generated from the engine according to the operating time and operating conditions.
Japanese Patent Laid-Open No. 04-203413 JP 60-47937 A

  In the method of transmitting light into the exhaust gas pipe and measuring the opacity as in the invention disclosed in Patent Document 1, the entire exhaust gas flow can be measured. There is a problem that accuracy deteriorates.

  Examining the method for determining the amount of particulate deposition based on the differential pressure disclosed in Patent Document 2, in the particulate collection filter, the filter pressure loss often has hysteresis with respect to the amount of particulate deposition. In many cases, it is impossible to uniquely detect the amount of accumulated particulate matter only from the differential pressure of the exhaust pressure before and after the filter due to loss. For example, in a wall flow type ceramic filter (DPF) that collects exhaust particulates of a diesel engine, after the particulates continue to be collected at a low temperature, the catalyst coated in the filter pores is temporarily activated at a temperature. When the temperature is raised to, the fine particles deposited in the pores are removed by oxidation, and the pressure loss significantly decreases due to the slight oxidation and disappearance of the fine particles in the fine pores. Therefore, the relationship between the amount of deposited fine particles and the pressure loss shows hysteresis, Even with the same pressure loss, the amount of deposited particulates can vary greatly. Therefore, in such a particulate collection filter, it is difficult to estimate the amount of particulate deposition uniquely from the pressure loss.

  There is also a problem that neither the method for determining the amount of fine particle deposition based on the differential pressure nor the modeling method directly detects the amount of fine particle deposition.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a sensor that can be used for on-vehicle diagnosis of fine particles.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by a specific fine particle sensor provided with an electrode, and have completed the present invention.

  That is, according to the present invention, the following fine particle sensor and fine particle measurement method are provided.

[1] Particulate collection means for collecting fine particles on a part of a cross section perpendicular to the gas flow path or a second flow path different from the gas flow path, and at least two electrodes provided in the fine particle collection means Fine particle sensor with

[2] The particulate sensor according to [1], wherein the particulate collection means is a honeycomb structure.

[3] The particulate sensor according to [2], wherein the honeycomb structure is a particulate collection filter.

[4] The particulate sensor according to [1], wherein the particulate collection means is ceramic foam.

[5] A fine particle amount determination method in which a direct current is passed between the electrodes of the fine particle sensor according to any one of [1] to [4], and the fine particle amount is determined based on a direct current resistance between the electrodes.

[6] A method for determining the amount of fine particles, wherein an alternating current is passed between the electrodes of the fine particle sensor according to any one of [1] to [4], and the amount of fine particles is determined based on impedance between the electrodes.

  The particulate sensor of the present invention can detect particulates without increasing pressure loss. The fine particle sensor of the present invention is disposed in a part of the cross section of the gas flow path or a second flow path different from the gas flow path. Therefore, the particulate collection means constituting the particulate sensor of the present invention does not block the entire cross section of the gas flow path. For this reason, even if a particulate collection filter (DPF) having a relatively large pressure loss is used as the particulate collection means, the pressure loss can be kept low.

  In addition, since the particle sensor of the present invention is smaller than the particle sensor that covers the entire cross section of the gas flow path, it can be manufactured at low cost.

  ADVANTAGE OF THE INVENTION According to this invention, the sensor which can detect a small amount of microparticles | fine-particles reliably and can judge whether the regulation is cleared on a vehicle is provided.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

  FIG. 1 is a schematic side view showing an embodiment of the present invention. The fine particle sensor 2 includes a fine particle collecting means 4 and electrodes 6 provided on part of the upper and lower surfaces of the fine particle collecting means 4. The particulate sensor 2 collects particulates in a part of the cross section of the gas flow path 8. The gas flow 10 flows from left to right in FIG.

  FIG. 2 is a schematic side view showing another embodiment of the present invention. The fine particle sensor 2 includes a fine particle collecting means 4 and electrodes 6 provided on part of the upper and lower surfaces of the fine particle collecting means 4. The fine particle sensor 2 collects fine particles in a flow channel 12 different from the gas flow channel 8. The gas flow 10 flows from left to right in FIG.

  Various means can be adopted as the particulate collection means in the present invention.

  In the present invention, the material of the particulate collecting means (excluding the electrode) is not particularly limited, but silicon carbide, cordierite, alumina titanate, sialon, mullite, silicon nitride, zirconium phosphate, zirconia, titania, alumina or silica or What is comprised from the ceramic which consists of these combinations, or the material which has a sintered metal as a main component is suitable.

  The shape of the fine particle collecting means may be any shape as long as the fine particle can be collected. Examples of preferable shapes include a honeycomb shape, a fine particle collection filter (DPF) shape, and a ceramic foam shape, but are not limited thereto.

  A honeycomb structure can be exemplified as a honeycomb-shaped one. Here, the honeycomb structure means a structure having a large number of flow holes (cells) penetrating in the axial direction partitioned by partition walls. In the present invention, the particulate collection filter (DPF) refers to a filter in which one end of each cell is alternately plugged so as to form a staggered pattern on the end face of the honeycomb structure.

  In the present invention, the ceramic foam body is a ceramic whose base material is silicon carbide, cordierite, alumina titanate, sialon, mullite, silicon nitride, zirconium phosphate, zirconia, titania, alumina, silica, or a combination thereof. A porous material such as foamed polyurethane foam is kneaded and fired in the clay, and the finished molded product has a porosity of 75% or more.

  The size of the cross-section of the particulate collection means of the present invention is not limited as long as the entire cross section of the gas flow path is blocked, but is preferably 50% or less of the cross section of the gas flow path. You may use the segment which consists of a several cell used when manufacturing a particulate collection filter (DPF) as a particulate collection means of this invention. Furthermore, a single cell may be used as the particulate collection means of the present invention.

  The fine particle sensor of the present invention can detect the amount of collected fine particles by using an electrode. Specifically, the amount of collected fine particles is detected by measuring electrical characteristics such as AC impedance, DC resistance, reactance, and capacitance between the electrodes. That is, in this fine particle sensor, the capacitance between the electrodes and the DC resistance value due to the accumulation of fine particles on the fine particle sensor by measuring the electrical characteristics such as the AC impedance between the electrodes provided in the fine particle sensor. Etc. can be detected. Since the capacitance between the electrodes changes corresponding to the absolute amount of fine particles in the fine particle sensor, it is possible to uniquely estimate the fine particle accumulation amount of the fine particle sensor from measurement data of electrical characteristics such as AC impedance. it can. Specifically, by preliminarily graphing the relationship between the mass of the deposited fine particles and the electrical characteristics such as AC impedance based on the actual measurement values, simply measuring the electrical characteristics such as AC impedance, It becomes possible to estimate the amount of deposited fine particles at the time of measurement.

  In the present invention, it is possible to estimate the amount of deposited fine particles from the measured value of AC impedance in this way, but in order to determine the amount of deposited fine particles more accurately, a coil (inductance) is provided in the impedance measuring circuit. Are preferably connected. By connecting the coils in this way, the AC impedance of the circuit including the coil and the filter having the electrostatic capacitance is the resonance condition Lω = 1 / Cω (L: inductance, C: electrostatic capacitance, ω: 2πf (f: Since the frequency)) suddenly approaches 0, the change in the AC impedance with respect to the change in the amount of deposited fine particles becomes sharp, and the amount of deposited particles can be detected more accurately.

  The inductance value of the coil to be connected may be set so as to satisfy the resonance condition in the target particle deposition amount. That is, by using a variable inductance, the inductance value is controlled in advance so that the AC impedance abruptly approaches 0 when the amount of deposited particles reaches a predetermined value. In the present invention, it is possible to adjust resonance conditions by connecting capacitance, DC resistance, etc. in series or in parallel in the impedance measurement circuit in addition to such inductance.

  In the fine particle sensor of the present invention, the frequency of the alternating current when measuring the alternating current impedance is preferably 1 kHz to 10 MHz. If it is less than 1 kHz, the ratio of the DC resistance component occupying the impedance increases, so the relative change rate of the measured impedance due to the change in capacitance decreases, and the accuracy of detecting the amount of deposited particles decreases. On the other hand, if it exceeds 10 MHz, the amount of noise-like inductance included in the entire measurement system including the signal extraction line from the fine particle sensor becomes excessive, and the measurement accuracy decreases.

In the present invention, the amount of particulates (PM) deposited can be determined by detecting the direct current resistance of the honeycomb structure having conductivity. For this purpose, it is preferable that the conductivity of the particulate collecting means is 1.0 × 10 ⁻⁶ S / cm or more at room temperature (25 ° C.), and the change in conductivity at 25 ° C. to 800 ° C. is 2 digits or less. . As such a particulate collecting means, a honeycomb structure mainly composed of Si-bonded SiC can be exemplified. Here, in this specification, a main component means what occupies 60 mass% or more of a component.

  In the present invention, the material of the electrode is not particularly limited, but is preferably composed of a sintered body of conductive paste, conductive ceramics, or metal.

  In the fine particle sensor of the present invention, the method of forming the electrode is not particularly limited. However, when a method of applying a conductive paste such as silver paste to a predetermined position on the outer peripheral surface of the fine particle sensor and heating and baking it is formed. It is preferable because it is easy and the electrode is firmly bonded to the fine particle sensor.

In addition, it is preferable to select each material so that the difference between the thermal expansion coefficients of the fine particle collecting means and the electrode is 20 × 10 ⁻⁶ / ° C. or less. For example, when the particulate sensor of the present invention is used directly under an engine, it is exposed to a high temperature environment during use. Therefore, if the difference in thermal expansion coefficient between the particulate collection means and the electrode is too large, There is a risk that the particle sensor may be damaged or the electrode may be peeled off due to the difference in expansion. However, if the difference in thermal expansion coefficient between the two is 20 × 10 ⁻⁶ / ° C. or less, the possibility of such a problem is low. Become.

  In the present invention, two or more electrodes may be formed in a flat plate shape arranged in parallel, and at least one of the electrodes may be configured by disposing a conductor inside the ceramic body. Good. In this manner, by configuring the conductor to be covered with the ceramic body, the conductor does not directly contact the exhaust gas, and it is possible to effectively prevent the conductor from being corroded or deteriorated. Furthermore, you may comprise both electrodes with the ceramic body and the conductor arrange | positioned in the inside.

The fine particle sensor of the present invention may or may not carry a catalyst on a substrate. In the present invention, the catalyst may be a three-way catalyst, an oxidation catalyst, a NO _X selective reduction catalyst (SCR), a NO _X storage reduction catalyst (LNT), or the like.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Example 1)
Talc, kaolin, calcined kaolin, alumina, aluminum hydroxide, the respective powders of silica, SiO ₂ is 42 to 56 wt%, _Al 2 _{O 3} is 0 to 45 wt%, MgO is the chemical composition of 12 to 16 wt% To the cordierite forming raw material prepared at a predetermined ratio so as to fall within the range of 15 to 25% by mass of graphite as a pore-forming agent, 5 to 15% by mass in total of synthetic resins such as PET, PMA, and phenol resin, Further, methylcelluloses and a surfactant were added in predetermined amounts, and water was added thereto and kneaded to obtain a clay. The clay is then vacuum degassed, extruded into a honeycomb structure, dried by microwave drying and hot air drying, and fired at a maximum temperature of 1400 to 1435 ° C. ) In the shape of a rectangular parallelepiped.

  An electrode was formed by applying and baking a silver paste at two opposing locations on the outer periphery of the honeycomb structure to constitute an impedance measurement circuit for measuring the AC impedance between the electrodes.

  The fine particle sensor 2 composed of this electrode-equipped honeycomb structure was disposed in the gas flow path 8 as shown in FIG. While the diesel engine exhaust gas containing fine particles was flowed into the gas flow path 8 and the ac impedance between the electrodes was measured while depositing the fine particles on the fine particle sensor 2, the mass of the accumulated fine particles and the measured ac impedance The relationship is as shown in FIG. 3, and it was confirmed that the amount of deposited fine particles can be estimated from the value of AC impedance.

  FIG. 3 is a diagram showing impedance measurement results (surface electrode, electrode size diameter 20 mm, 10 kHz) at the location of the particle sensor 2 of the present invention shown in FIG. In FIG. 3, the horizontal axis represents the amount of deposited fine particles (mg / L), and the vertical axis represents the impedance change rate (%).

(Example 2)
For 100% by mass of SiC powder having an average particle size of 20 μm containing 16% by mass of particles having a particle size of 5 μm or less, 5% by mass of gyrome clay, 3% by mass of methylcellulose, 1% by mass of surfactant, and 25% by mass of water After mixing, a honeycomb-shaped formed body having a side length of 30 mm, a length of 150 mm, a cell density of 16 cells / cm ² and a rib thickness of 430 μm was formed by extrusion molding. This molded body was calcined at 400 ° C. in an oxidizing atmosphere to remove the binder component, and then fired at 2200 ° C. in an Ar atmosphere to obtain a recrystallized SiC sintered body having a honeycomb structure.

  A silver paste was applied and baked at two opposing locations on the outer periphery of the honeycomb structure to form an electrode, and a DC resistance measuring circuit for measuring the DC resistance between the electrodes was configured.

  The fine particle sensor 2 composed of this electrode-equipped honeycomb structure was disposed in the gas flow path 8 as shown in FIG. When the diesel engine exhaust gas containing fine particles is caused to flow through the gas flow path 8 and the direct current resistance between the electrodes is measured while the fine particles are deposited on the fine particle sensor 2, the mass of the accumulated fine particles, the measured direct current resistance, The relationship is as shown in FIG. 4, and it was confirmed that the amount of deposited fine particles can be estimated from the value of DC resistance.

  FIG. 4 is a diagram showing a DC resistance measurement result (surface electrode, electrode size diameter 20 mm) at the location of the particle sensor 2 of the present invention shown in FIG. In FIG. 4, the horizontal axis indicates the amount of deposited fine particles (g / L), and the vertical axis indicates the DC resistance change rate (%).

  The present invention can be used as a particulate sensor that measures the amount of particulates discharged in an exhaust system of an internal combustion engine.

It is a schematic side view which shows one Embodiment of this invention. It is a schematic side view which shows other one Embodiment of this invention. It is a figure which shows the impedance measurement result in the place of the fine particle sensor of this invention shown in FIG. It is a figure which shows the direct current | flow resistance measurement result in the place of the fine particle sensor of this invention shown in FIG.

Explanation of symbols

2: Fine particle sensor, 4: Fine particle collecting means, 6: Electrode, 8: Gas flow path, 10: Gas flow, 12: Another gas flow path

Claims (6)

Fine particle collecting means for collecting fine particles on a part of a cross section perpendicular to the gas flow path or a second flow path different from the gas flow path;
A particulate sensor comprising at least two electrodes provided in the particulate collection means.   The particulate sensor according to claim 1, wherein the particulate collection means is a honeycomb structure.   The particulate sensor according to claim 2, wherein the honeycomb structure is a particulate collection filter.   The particulate sensor according to claim 1, wherein the particulate collection means is ceramic foam.   A method for determining the amount of fine particles, wherein a direct current is passed between the electrodes of the fine particle sensor according to claim 1, and the amount of fine particles is determined based on a direct current resistance between the electrodes.   A method for determining the amount of fine particles, wherein an alternating current is passed between the electrodes of the fine particle sensor according to any one of claims 1 to 4 and the amount of fine particles is determined based on an impedance between the electrodes.

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